1. Field of the Invention
The present invention relates to a direction of arrival estimator and direction of arrival estimation method for estimating the direction of arrival of a reception signal using an array antenna.
2. Description of the Related Art
As a method for improving the reception quality of a base station apparatus in a radio communication system, a method of estimating the direction of arrival of a reception signal with an array antenna incorporated and focusing directivity on a desired signal is proposed. Since a signal received by the base station apparatus includes a multitude of interference signals in addition to the desired signal, the base station apparatus needs to separate all signals included in the reception signal and select the desired signal in order to estimate the direction of arrival of the desired signal.
When the base station apparatus carries out radio communication with a plurality of terminal apparatuses using a spread spectrum signal, the base station apparatus can separate all signals included in the reception signal by carrying out despreading processing, etc.
Here, there are cases where within the frequency band of a spread spectrum signal, a signal of a narrow frequency band is mixed with the spread spectrum signal such as a frequency-modulated signal and received by an antenna.
In this case, the base station apparatus cannot separate the spread spectrum signal, a desired signal, from the other signal, an interference signal, and therefore it is necessary to separate the desired signal from the interference signal in some way to estimate the direction of arrival of the desired signal.
However, no technology has been disclosed so far to distinguish the spread spectrum signal from a reception signal made up of the spread spectrum signal and a signal based on a modulation system different from that of the spread spectrum signal.